1. Field of the Invention
The invention relates to a film capacitor and in particular to a film capacitor with excellent heat resistance, heat dissipation, and workability.
2. Description of Related Art
Conventionally, due to an electrical characteristic of a high withstand voltage and low loss, a metalized film capacitor (also referred to as a metal-deposited-electrode type capacitor) in which metal such as aluminum is deposited on a surface of a dielectric film made of polypropylene or the like has been used in various industrial fields including a home appliance industry and an automotive industry.
It has been known that an electrostatic capacitance of this type of the film capacitor greatly depends on a temperature and that the electrostatic capacitance decreases with a temperature increase. It has also been known that, for example, in the case where large high-frequency noise, an in-rush current, a short-circuit current, or a lightning surge current flows through the capacitor during use and an operating temperature increases, a crack is produced on the inside of the dielectric film when the temperature of the capacitor returns from a high temperature to a room temperature or the like. Accordingly, a leakage current increases, and the capacitor can no longer withstand a high electric field. As a result, the withstand voltage decreases.
To address such a problem, Japanese Patent Application Publication No. 2007-19327 (JP 2007-19327 A) describes a high heat resistance film capacitor which has a capacitor element constituted by a dielectric film and a conductor, and in which a synthetic polymer compound contained in the dielectric film contains insulating ceramic fine particles with thermal conductivity of 4 W/m·K or higher.
In the high heat resistance film capacitor described in JP 2007-19327 A, the synthetic polymer compound contained in the dielectric film contains the insulating ceramic fine particles with the thermal conductivity of 4 W/m·K or higher. Thus, the film capacitor has excellent heat resistance and heat dissipation. In addition, rated capacitance can be increased by increasing current density. Furthermore, a cooling device (a fan or a heat sink) or the like does not need to be provided. Thus, a configuration of the capacitor is simplified. As a result, downsizing and cost reduction can be achieved.
However, in the high heat resistance film capacitor described in JP 2007-19327 A, the dielectric film contains the synthetic polymer compound, which contains the insulating ceramic fine particles composed of aluminum nitride, beryllium oxide, alumina, silicon carbide, diamond, boron nitride or the like, in a state where the synthetic polymer compound is dispersed over the entire dielectric film. Thus, toughness of the dielectric film itself decreases and workability thereof decreases (for example, in the case where the toughness of the dielectric film is low, the dielectric film may break due to stress applied to the dielectric film when evaporated metal is deposited on a surface of the dielectric film), and production cost increases.